Adequate delivery of mechanical ventilation in spontaneously breathing patients is difficult to determine unless information about the patient's respiratory drive and load is known.
Methods to determine the respiratory drive using electrical activity of the diaphragm EAdi (also referred to as diaphragm electomyogram EMG) have been previously proposed as well as the use of these methods to control ventilatory assist (U.S. Pat. Nos. 5,820,560; 6,962,155; 7,021,310).
Previous methods to determine the passive elastic and resistive respiratory load have also been described, for example in U.S. Pat. No. 5,884,622, to control the so-called proportional assist ventilation by applying the equation of motion as described in U.S. Pat. No. 5,107,830.
A limitation of the current methods for determining the load imposed on the patient's respiratory system resides in use of an assumption that respiratory muscles are inactive during expiration, which is not always the case.